Film formation method, mask for film formation and film formation device

ABSTRACT

A film formation method is provided for masking a part of a surface of an object and subsequently forming a film, by a chemical vapor deposition method, on a surface on which a film should be formed that is an exposed part of the surface of the object. The film formation method includes, upon film formation in a reaction chamber, masking the object by using a mask having a gas path formed therewithin and vents connecting the gas path with an outer surface of the mask, and controlling concentration distribution of raw material substances in the reaction chamber so that a film formation rate in the surface on which a film should be formed is constant by discharging or attenuating raw material gases, using the gas path within the mask, supplied to a surface which is covered with the mask and on which no film is formed.

TECHNICAL FIELD

The present invention relates to a method for forming a film by aChemical Vapor Deposition (CVD) method and a mask used for a maskingstep in film formation.

BACKGROUND ART

The Chemical Vapor Deposition method is a method for forming a film byusing raw material gases by a chemical reaction. This method has a widerange of industrial applications from thin film formation inmicrodevices such as a semiconductor device to coating on objects havinga length greater than 1 m.

The Chemical Vapor Deposition method has recently been also used formanufacturing display panels having a large screen with a diagonal sizeequal to or more than 1 m. U.S. Pat. No. 6,450,849 describes a methodfor manufacturing an AC plasma display panel in which a dielectric layerfor covering electrodes is formed by a plasma CVD method. The ChemicalVapor Deposition method makes it possible to obtain a dielectric layerhaving a small and uniform thickness. Compared to a thick film method,the Chemical Vapor Deposition method can form, at a low temperature, adielectric layer made of, for example, silicon dioxide or organicsilicon oxide having a dielectric constant lower than that of alow-melting point glass that is a general material.

In general, a film formation device used for forming a film by theChemical Vapor Deposition method is designed to supply raw materialsubstances equally to a surface on which a film should be formed. Forexample, Japanese unexamined patent publication No. 11-350143 describesa parallel plate plasma CVD system. In the system, a shower plate whosethickness is purposely uneven is disposed between a gas inlet port of areaction chamber and a surface on which a film should be formed. Theshower plate is a nozzle that injects a gas to the entire surface onwhich a film should be formed and has many micro injection holes. Theshower plate uses the fact that a gas flow rate of an injection holedepends on the length of the injection hole. Then, thicknesses of theshower plate at various positions are so selected that a gas injectionrate at the center of the shower plate is equal to a gas injection ratein ends of the shower plate.

For film formation by the Chemical Vapor Deposition method, in the casewhere an object on which a film should be formed has a part on whichfilm formation is unnecessary, masking is performed on the part.Japanese unexamined patent publication No. 11-269646 discloses atechnique of performing masking using a jig having a coefficient ofthermal expansion that is substantially the same as that of an object onwhich a film should be formed.

DISCLOSURE OF THE INVENTION

In the manufacture of a plasma display panel in which the Chemical VaporDeposition method is used to form a dielectric layer on a substrate inwhich electrodes are arranged, unfortunately, a thickness of adielectric layer becomes uneven when masking is performed with thesubstrate being covered with a mask in order to expose terminal portionsof the electrodes. Specifically, such masking causes the vicinity of themask to be thicker than the other parts.

The uneven thickness of the dielectric layer causes variations inoperating characteristics of cells constituting a screen. It isdesirable that the thickness of the dielectric layer be uniform forhigh-quality display in a stable manner.

The present disclosure is directed to solve the problems pointed outabove, and therefore, an object of an embodiment of the presentinvention is to provide a uniform film thickness in film formationincluding a masking step.

According to one aspect of the present invention, a film formationmethod for masking a part of a surface of an object and subsequentlyforming a film, by a chemical vapor deposition method, on an exposedpart without any mask of the surface of the object, the film formationmethod includes masking the object by using a mask when film formationis performed in a reaction chamber, the mask having a gas path formedwithin the mask and vents connecting the gas path with an outer surfaceof the mask, and controlling concentration distribution of raw materialsubstances in the reaction chamber so that a film formation rate in thesurface on which a film should be formed is constant by discharging orattenuating raw material gases, using the gas path within the mask,supplied to a surface which is covered with the mask and on which nofilm is formed.

These and other characteristics and objects of the present inventionwill become more apparent by the following descriptions of preferredembodiments with reference to drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an example of a cellstructure of a plasma display panel.

FIG. 2 is a plan view showing a pattern of display electrodes.

FIG. 3 is a diagram showing an area where masking is necessary when adielectric layer is formed in the manufacture of a plasma display panel.

FIG. 4 is a plan view showing a mask used in the manufacture of a plasmadisplay panel.

FIG. 5 is a sectional diagram taken along the line a-a of FIG. 4.

FIG. 6 is a schematic diagram showing the outline of a film formationdevice according to a first embodiment.

FIG. 7 is a plan view showing another example of a mask used in themanufacture of a plasma display panel.

FIG. 8 is a schematic diagram showing the outline of a film formationdevice according to a second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a description of a film formation method according tothe present invention. In the description, formation of a dielectriclayer of a plasma display panel is exemplified.

First Embodiment

FIG. 1 is an exploded perspective view showing an example of a cellstructure of a plasma display panel. Referring to FIG. 1, a front panel10 and a rear panel 20 are separated from each other for easyunderstanding of the inside structure of the plasma display panel.

The plasma display panel 1 is made up of the front panel 10 and the rearpanel 20. The front panel 10 includes a glass substrate 11, displayelectrodes X and Y, a dielectric layer 17 and a protection film 18. Eachof the display electrodes X and Y is a laminate including a patternedtransparent conductive film 41 and a patterned metal film 42. Thedisplay electrodes X and Y are covered with the dielectric layer 17 andthe protection film 18. The rear panel 20 includes a glass substrate 21,address electrodes A, an insulation layer 24, a plurality of partitions29 and fluorescent material layers 28R, 28G and 28B. The illustratedarrangement pattern of the partitions 29 is a stripe pattern. Each ofthe alphabets R, G and B in parentheses shown in the drawing representsa light emission color of a fluorescent material.

FIG. 2 is a pattern of the display electrodes. The display electrodes Xand the display electrodes Y that make an electrode group 40 areextended from a screen 60 to a vicinity of a periphery of the glasssubstrate 11. Each of the display electrodes X and Y has on its end aterminal X_(t) or Y_(t) for conductive connection to a drive unit.Referring to FIG. 2, the terminals X_(t) of the respective displayelectrodes X are disposed on the left side of the glass substrate 11while the terminals Y_(t) of the respective display electrodes Y aredisposed on the right side thereof. The arrangement pitch of theterminals X_(t) is different from that of the display electrodes X inthe screen 60; therefore the left end portions including the terminalsX_(t) of the display electrodes X are patterned to have a bentribbon-like shape. The bent portions are made up of only the metal film42 rather than the laminate of the transparent conductive film 41 andthe metal film 42. Likewise, the right end portions including theterminals Y_(t) of the display electrodes Y are patterned to have a bentribbon-like shape. The bent portions are made up of only the metal film42.

The plasma display panel 1 of this type is manufactured by making thefront panel 10 and the rear panel 20 separately, and then, bonding thefront panel 10 and the rear panel 20 together. A mother glass substratewhose area is twice or more as large as the glass substrate 11 is usedto make a plurality of the front panels 10 at one time. A plurality ofthe rear panels 20 is formed at one time in the same manner. Beforebonding the front panel 10 and the rear panel 20 together, a motherglass substrate is divided into a plurality of the front panels 10 or aplurality of the rear panels 20. Then, the front panel 10 separated froma mother glass substrate is bonded to the rear panel 20 separated from amother glass substrate, so that the front panel 10 and the rear panel 20are integrated with each other. Upon making the front panel 10, thedielectric layer 17 is formed by a Chemical Vapor Deposition method.During this process, masking is performed on the terminals X_(t) andY_(t).

If no masking is performed, it is necessary, after forming thedielectric layer 17, to remove a part of the dielectric layer 17 byetching or grinding and to expose the terminals X_(t) and Y_(t). Themasking step eliminates the need for the step of removing the dielectriclayer 17. This shortens manufacturing time, increases a yield, andimproves productivity.

FIG. 3 is a diagram showing an area where masking is necessary when adielectric layer is formed in the manufacture of a plasma display panel.

Referring to FIG. 3, two electrode groups 40 are formed on a motherglass substrate 111 in the form of two lines. A section of the motherglass substrate 111 in which one of the two electrode groups 40 isplaced corresponds to the glass substrate 11 on the front side of oneplasma display panel. Areas of the mother glass substrate 111 wheremasking is necessary are areas S11 corresponding to terminals of theelectrode groups 40 shown in the upper part of the drawing and areas S12corresponding to terminals of the electrode groups 40 shown in the lowerpart of the drawing.

FIG. 4 is a plan view showing a mask used in the manufacture of a plasmadisplay panel, and FIG. 5 is a sectional diagram taken along the linea-a of FIG. 4.

A mask 71 is a frame-like member made of aluminum having a thickness ofapproximately 30 mm. The mask 71 has two rectangular openings 711 and712 necessary to form dielectric layers for two plasma display panels atone time. The mask 71 has a contour and a thickness greater than thoseof the mother glass substrate. Accordingly, the mask 71 has sufficientmechanical strength to function as a pressing member for preventing themother glass substrate from warping due to heating.

A peripheral surface of each of the openings 711 and 712 is formed tohave a tapered shape in which an upper part of the opening is broadened,which avoids generating a part where nothing is deposited. A stepportion is formed around the opening in order that a lower end of theperipheral surface is away from the upper surface of the electrode group40 by approximately 0.5 mm to 1.0 mm. The step portion causes the motherglass substrate and the mask to be in a non-contact state, therebypreventing the terminals and terminal lead-out portions (bent portionsof the ends of the display electrodes) from being scratched.

The mask 71 has, as elements unique to the present invention, a gas path75 and a plurality of vents 76. The gas path 75 and the vents 76 areprovided in an area between the openings 711 and 712.

As shown in FIG. 5, the gas path 75 is formed within the mask 71 and hasa length over the entire length of the opening 711 or 712 in thelongitudinal direction. End portions 751 and 752 of the gas path 75communicate with the outer peripheral surface of the mask 71, so thatthe end portions 751 and 752 can connect to piping of an exhaust system(not shown).

The vents 76 are arranged at almost regular intervals in the form of oneline along the gas path 75. Each of the vents 76 communicates with thegas path 75 and the front face of the mask 71 as shown in FIG. 5.

Examples of a method for making the mask 71 are a method of forming thegas path 75 and the vents 76 by a machining process and a method ofmaking parts of the mask 71 separately and combining the resultant partsto form the gas path 75 as a groove.

FIG. 6 is a schematic diagram showing the outline of a device used forforming a dielectric layer by a Chemical Vapor Deposition method.

A parallel plate plasma CVD system 300 is used for forming a dielectriclayer (hereinafter referred to as film formation). The plasma CVD system300 includes a reaction chamber 310 that is a container made of metal, ashower nozzle 320 functioning also as an electrode for generatingplasma, a movable base 330 for supporting an object on which a filmshould be formed and the mask 71 for masking as described above. Themovable base 330 has a heater, incorporated therein, for heating theobject.

The mask 71 is placed between the shower nozzle 320 and the movable base330 within the chamber 310. The gap size between the mask 71 and theshower nozzle 320 is approximately 10 mm to 20 mm. In the illustratedexample, the mother glass substrate 111 in which the electrode groups 40are formed is placed on the movable base 330 and the mother glasssubstrate 111 is covered with the mask 71.

In this example, the movable base 330 is of a lift type capable ofmoving in the vertical direction. When the mother glass substrate 111 isbrought in or carried out, the movable base 330 goes down and isdistanced from the mask 71 fixedly placed.

The following is a description of the outline of a film formationprocess.

Raw material gases are provided from an inlet port 321 formed at thecenter of the shower nozzle 320 to the chamber 310 in the state in whichthe internal pressure of the chamber 310 in which the mother glasssubstrate 111 is brought is reduced to a pressure of, for example,approximately 2.5 Torr to 3.5 Torr and the mother glass substrate 111 isheated up to a temperature of approximately 200° C. to 400° C. In thecase where a dielectric layer made of silicon dioxide is formed, forexample, silane (SiH₄) is provided as a source gas and, for example,nitrous oxide (N₂O) is provided as a reaction gas. The raw materialgases thus provided are injected from the shower nozzle 310 to theentire mother glass substrate 111 substantially uniformly.

The chamber 310 is exhausted through a main exhaust hole 311,concomitantly with the provision of the raw material gases. The chamber310 is provided with a vacuum gauge (not shown). A valve of the exhaustsystem is controlled in accordance with the output of the vacuum gauge;thereby a vacuum level of the chamber 310 is maintained at a constantlevel.

In the chamber 310 to which a constant amount of the raw material gasesis supplied as described above, plasma generated by applying ahigh-frequency power activates the raw material gases, leading to thepromotion of a chemical reaction. Then, raw material substancesgenerated by the chemical reaction deposit on a surface S1 on which afilm should be formed of the mother glass substrate 111, so that a film,which eventually becomes a dielectric layer, is formed. The surface S1in this example is a non-masked portion of the upper surface of themother glass substrate 111 in which the electrode groups 40 are formed.In a precise sense, the surface S1 is made up of exposure surfaces ofthe electrode groups 40 and a substrate surface between the electrodes.

In the first embodiment, while such film formation is performed, a gaswithin the chamber 310 is continuously or intermittently sucked into thegas path 75 within the mask 71. Specifically, the exhaust systemconnected to the end portions 751 and 752 (see FIG. 5) of the gas path75 is used to increase the vacuum level of the gas path 75 compared tothe vacuum level outside the mask 71.

The exhaust system used for the suction may be of a type that uses avacuum pump of an exhaust system for suction from the main exhaust hole311 or of a type that has a special vacuum pump. In the case of usingthe vacuum pump of the exhaust system for suction from the main exhausthole 311, a special valve is provided for independently adjusting anamount of gas to be sucked into the gas path 75.

The gas sucked into the gas path 75 contains unreacted raw materialgases and raw material substances that are generated by a chemicalreaction and do not deposit.

The suction of gas into the gas path 75 contributes to achievement ofuniform thickness of a film formed on the surface S1. The following is areason why uniform thickness of a film is achieved. Few raw materialsubstances deposit on the mask 71. Stated differently, compared to thefilm formation rate in the surface S1, the film formation rate in themask surface is very low. Unless the suction is performed, raw materialgases injected by the shower nozzle 320 to the mask 71 and raw materialsubstances generated between the shower nozzle 320 and the mask 71 flowto the surface S1. Consequently, the concentration of the raw materialsubstances are locally increased at a portion of the surface S1 close tothe mask 71 and the film formation rate in the portion is higher thanthat of the other portions of the surface S1. The appropriate suction ofgas into the gas path 75 reduces or eliminates the excess supply of gasfrom a space between the shower nozzle 320 and the mask 71 to a spacebetween the shower nozzle 320 and the surface S1, thereby making itpossible to equalize the film formation rate in the surface S1.

In the plasma CVD system 300 according to this embodiment, the mask 71is placed just below a position at which the inlet port 321 of theshower nozzle 320 is provided. At the position, the injection amount ofthe raw material gases tends to be large compared to that at the otherpositions of the shower nozzle 320. Accordingly, it is effective inequalizing a thickness of a film to be formed to suck the raw materialgases into the mask 71 just below the position.

Second Embodiment

FIG. 7 is a plan view showing another example of the mask used in themanufacture of a plasma display panel.

The basic structure of a mask 72 shown in FIG. 7 is the same as that ofthe mask 71 described earlier with reference to FIG. 4. Similarly to themask 71, the mask 72 also has two rectangular openings 721 and 722necessary to form dielectric layers for two plasma display panels at onetime.

The mask 72 has, as elements unique to the present invention, a gas path77 and a plurality of vents 78. The gas path 77 and the vents 78 areprovided in an area between the openings 721 and 722.

The gas path 77 is formed within the mask 72 and has a length over theentire length of the opening 721 or 722 in the longitudinal direction.End portions 771 and 772 of the gas path 77 communicate with the outerperipheral surface of the mask 72, so that the end portions 771 and 772can connect to piping of a gas supply system (not shown).

The vents 78 are arranged at almost regular intervals in the form of twolines along the gas path 77. Each of the vents 78 communicates with thegas path 77 and the front face of the mask 72.

FIG. 8 is a schematic diagram showing the outline of a film formationdevice according to the second embodiment. In FIG. 8, similar referencenumerals are used to denote elements similar to those of the deviceshown in FIG. 6. Description of these elements is omitted.

A plasma CVD system 301 shown in FIG. 8 has the same structure as thatof the plasma CVD system 300 shown in FIG. 6 except in that the plasmaCVD system 301 includes a mask 72 instead of the mask 71 in the plasmaCVD system 300.

In the second embodiment, while the plasma CVD system 301 is used toform a film, inert gases are continuously or intermittently provided tothe chamber 310 through the gas path 77 and the vents 78, concomitantlywith the provision of the raw material gases. Argon (Ar) and nitrogen(N₂) are suitable inert gases.

Providing the inert gases from the gas path 77 has an effect ofattenuating the raw material gases locally in the vicinity of the mask72. Providing the inert gases appropriately reduces or eliminates thelocal increase in the concentration of raw material substances, whichoccurs at a part close to the mask 72, thereby making it possible toequalize the film formation rate in the surface S1.

In the first and second embodiments described above, the cases in whichthe vents 76 or 78 are formed only in an area between the two openingsof the mask 71 or 72 are exemplified. The present invention, however, isnot limited to the cases. The vents 76 or 78 may be formed at a partnecessary to equalize the film thickness depending on the structure of afilm formation device. For example, in the case of a film formationdevice configured to supply raw material gases equally to the entiresurface of an object on which a film should be formed, a gas pathpassing through the entire periphery of an opening of a mask is formedand vents are arranged along the entire periphery of the opening.

Either one or both of the size and density of the vents 76 or 78 may beoptimized depending on the positions where the vents 76 or 78 arearranged. Stated differently, the present invention does not exclude acase in which the size and density of the vents 76 or 78 are different.

The shape, size, thickness, and material of each of the masks 71 and 72should be selected depending on purposes and can be changedappropriately. In the case where, for example, film formation isperformed for four, eight or more plasma display panels at one time, amask having an appropriate size is used.

The present invention can be applied to film formation by not only aChemical Vapor Deposition method such as a plasma CVD method but also aChemical Vapor Deposition method such as a thermal CVD method or anoptical CVD method.

INDUSTRIAL APPLICABILITY

The present invention can be applied to film formation in which a maskhaving a size large enough to form a gas path therewithin is used. Thepresent invention can be used for manufacturing, for example, a flatpanel display such as a plasma display panel and a liquid crystal panel.

1. A film formation method for masking a part of a surface of an objectand subsequently forming a film, by a chemical vapor deposition method,on an exposed part without any mask of the surface of the object, thefilm formation method comprising: masking the object by using a maskwhen film formation is performed in a reaction chamber, the mask havinga gas path formed within the mask and vents connecting the gas path withan outer surface of the mask; and controlling concentration distributionof raw material substances in the reaction chamber by using the gaspath.
 2. A film formation method for masking a part of a surface of anobject and subsequently forming a film, by a chemical vapor depositionmethod, on an exposed part without any mask of the surface of theobject, the film formation method comprising: masking the object byusing a mask when film formation is performed in a reaction chamber, themask having a gas path formed within the mask and vents connecting thegas path with an outer surface of the mask; and during performing thefilm formation, sucking a gas in the reaction chamber from the ventsinto the gas path.
 3. A film formation method for masking a part of asurface of an object and forming a film, by a chemical vapor depositionmethod, on a part exposed by masking the part of the surface of theobject, the film formation method comprising: masking the object byusing a mask when film formation is performed in a reaction chamber, themask having a gas path formed within the mask and vents connecting thegas path with an outer surface of the mask; and during performing thefilm formation, providing an inert gas to the reaction chamber throughthe gas path and the vents, concomitantly with providing a raw materialgas to the reaction chamber.
 4. A mask used for a masking step in filmformation by a chemical vapor deposition method, the mask comprising: agas path formed within the mask; and vents connecting the gas path withan outer surface of the mask.
 5. A film formation device for performingfilm formation by a chemical vapor deposition method, the devicecomprising a mask having a gas path formed within the mask and ventsconnecting the gas path with an outer surface of the mask.